What is a magnesium blood test?

A magnesium blood test measures the amount of magnesium in your blood. Magnesium is a type of electrolyte. Electrolytes are electrically charged minerals that are responsible for many important functions and processes in your body.

Your body needs magnesium to help your muscles, nerves, and heart work properly. Magnesium also helps control blood pressure and blood sugar.

Most of your body’s magnesium is in your bones and cells. But a small amount is found in your blood. Magnesium levels in the blood that are too low or too high can be a sign of a serious health problem.

Other names: Mg, Mag, Magnesium-Serum

What is it used for?

A magnesium blood test is used to check the level of magnesium in your blood. Levels that are too low are known as hypomagnesemia or magnesium deficiency. This is more common than levels that are too high, which is called hypermagnesemia.

A magnesium blood test is also sometimes included with tests of other electrolytes, such as sodium, calcium, potassium, and chloride.

Why do I need a magnesium blood test?

Your health care provider may order a magnesium blood test if you have symptoms of low magnesium or high magnesium levels.

Symptoms of low magnesium include:

  • Weakness
  • Muscle cramps and/or twitching
  • Confusion
  • Irregular heartbeat
  • Seizures (in severe cases)

Symptoms of high magnesium include:

  • Muscle weakness
  • Fatigue
  • Nausea and vomiting
  • Trouble breathing
  • Cardiac arrest, the sudden stopping of the heart (in severe cases)

You may also need this test if you are pregnant. A magnesium deficiency can be a sign of preeclampsia, a serious form of high blood pressure that affects pregnant women.

In addition, your provider may order this test if you have a health problem that can cause a magnesium deficiency. These include malnutrition, alcoholism, and diabetes.

What happens during a magnesium blood test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

Certain medicines can affect magnesium levels. Tell your health care provider about any prescription and over-the-counter medicines you are taking. Your provider will let you know if you need to stop taking them for a few days before your test. You’ll also need to stop taking magnesium supplements before your test.

Are there any risks to the test?

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

If your results show you have a magnesium deficiency, it may be a sign of:

  • Alcoholism
  • Malnutrition
  • Preeclampsia (if you are pregnant)
  • Chronic diarrhea
  • Digestive disorder, such as Crohn’s disease or ulcerative colitis
  • Diabetes

If your results show you have a higher than normal amount of magnesium, it may be a sign of:

  • Addison disease, a disorder of the adrenal glands
  • Kidney disease
  • Dehydration, the loss of too much bodily fluids
  • Diabetic ketoacidosis, a life-threatening complication of diabetes
  • Overuse of antacids or laxatives that contain magnesium

If your results show you have a magnesium deficiency, your health care provider will probably recommend you take magnesium supplements to raise levels of the mineral. If your results show you have too much magnesium, your provider may recommend IV therapies (medicine delivered directly to your veins) that can remove excess magnesium.

If you have questions about your results, talk to your health care provider.